Pipes made of thin-walled sheet metal are typically composed of sub-sections that are connected to one another. The method of connection crucially influences how economically the sub-sections can be produced and assembled. This also applies to pipe-shaped devices or devices comprising pipe-shaped connections, which must frequently be integrated in such pipes, and to pipe-shaped apparatuses comprising sub-sections.
With respect to the methods of connection, a differentiation is made between plug connections, which are predominantly used for smaller diameter pipes comprising sub-sections, and flanged connections. For these flanged connections, in general separate flanges are produced, which are screwed, riveted, welded or otherwise attached to the pipe end.
The flanges are produced by forming of the pipe end only in some cases.
The simplest way of an integrally formed flange is the stay flange, which is obtained by folding the edge of the pipe end at a right angle. In addition, crimpings are known, which are produced by rolling the pipe end into a bead that is substantially circular in its cross-section.
To connect these flanges configured as stay flanges or crimpings, tensioning rings having a U- or V-shaped cross-section are used, the clearance width of these rings being adjusted to the cross-section of the flanges bearing on one another. The tensioning rings must be considerably rigid because neither the stay flange nor the crimping sufficiently brace the pipe at the end in the radial direction. Higher radial rigidity is achieved with such integrally formed flanges that are created by folding up the pipe end twice at a right angle. Flanges of this type are used primarily for device housings, particularly the housings of radial fans. The flanges are connected to one another mostly be screws that are distributed across the circumference.
One of the more recent publications includes a method known from DE 100 47 310 A1 for integrally forming a flange to the end of a thin-walled pipe, which is first bent upward by 150° and then by 90°, thus creating a flange with a conical outer surface. The flanges bearing on one another on the abutment site of two pipe pieces can be connected by means of a tensioning ring having a V-shaped cross-section.
Due to drastically increased requirements with respect to tightness and smooth inside surfaces, particularly for the air ducts in ventilation, air conditioning and exhaust technology, increasingly pipes with integrally formed flanges are used. The disadvantage, however, is that the strength of the material forming the flange automatically only corresponds to the pipe wall thickness, which is frequently not sufficient for the required stability. To reinforce the flange, it has therefore been proposed, for example according to DE 102 15 112 C1, to slide a reinforcing ring on the end of the pipe section used for forming the flange, the ring doubling the wall thickness of the flange.
Frequently, however, even this type of reinforcement is not sufficient and not satisfactory.
It is therefore the object of the present invention to provide a method and a device for the integral forming of a flange to the end of a round or oval pipe made of thin-walled sheet metal, which allow a considerably stronger and considerably more stable flange to be produced. Such an object is achieved in that in a first stage, for the purpose of accumulating material, the end of an axial sub-section of the pipe is formed into a bead, while axially advancing a pre-forming roller tool at the same time, whereupon in a second stage the bead is compressed by means of a final-forming roller tool to produce a solid flange.